Bulbus glandis

The bulbus glandis (also called a bulb or knot) is an erectile tissue structure on the penis of canid mammals.[1][2][3][4][5][6] During mating, immediately before ejaculation the tissues swell up to lock (tie) the male's penis inside the female. The locking is completed by circular muscles just inside the female's vagina; this is called "the knot" tightening thus preventing the male from withdrawing. The circular muscles also contract intermittently, which has the effect of stimulating ejaculation of sperm, followed by prostatic fluid, as well as maintaining the swelling of the penis and therefore the tie, for some time. For domestic dogs the tie may last up to half an hour or more, though usually less.[7] When male canines are excited, the bulbus glandis may swell up inside the penile sheath, even if the dog has been neutered.[8]

Erect bulbus glandis (1) in a Labrador Retriever

The bulbus glandis also occurs in the penises of some pinnipeds, including South American fur seals.[9]

See alsoEdit


  1. ^ Howard E. Evans; Alexander de Lahunta (7 August 2013). Miller's Anatomy of the Dog - E-Book. Elsevier Health Sciences. ISBN 978-0-323-26623-9.
  2. ^ Kim Long (1996). Wolves: A Wildlife Handbook. Big Earth Pub. ISBN 978-1-55566-158-8. Retrieved 10 December 2012.
  3. ^ L. David Mech (16 May 2012). Wolf. Random House Digital, Inc. pp. 172–. ISBN 978-0-307-81913-0. Retrieved 10 December 2012.
  4. ^ Marshall Cavendish Corporation (1 September 2010). Mammal Anatomy: An Illustrated Guide. Marshall Cavendish. pp. 252–. ISBN 978-0-7614-7882-9. Retrieved 10 December 2012.
  5. ^ Debra A. Carlson (2008). Reproductive Biology of the Coyote (Canis Latrans): Integration of Behavior and Physiology. pp. 67–. ISBN 978-0-549-50315-6. Retrieved 9 February 2013.
  6. ^ H. M. Menino (2008). Darwin's Fox and My Coyote. University of Virginia Press. pp. 101–. ISBN 978-0-8139-2675-9. Retrieved 9 February 2013.
  7. ^ Susan Long (2006). Veterinary Genetics and Reproductive Physiology. Churchill Livingstone Elsevier. ISBN 978-0-7506-8877-2.
  8. ^ "Boy Dog Bumps - The Mysterious Bulbus Glandis". Clarendon Animal Care. March 8, 2018. Retrieved June 17, 2020.
  9. ^ Machado, Alex Sander D.; Bas, Le; Miglino, Maria Angélica; Leiser, Rudolf; Papa, Paula de Carvalho (1990-01-06). "Genital morphology of the male South American fur seal (Arctocephalus australis) and biological implications". Pesquisa Veterinária Brasileira. 32: 67–78. doi:10.1590/S0100-736X2012001300013. ISSN 0100-736X.